Stevia is a genus of about 240 species of herbs and shrubs in the sunflower family (Asteraceae), native to subtropical and tropical South America and Central America.
The species Stevia rebaudiana Bertoni, commonly known as sweet leaf, sugarleaf, or simply stevia, is widely grown for its sweet leaves. The leaves have traditionally been used as a sweetener. Steviosides and rebaudiosides are the major constituents of glycosides found in the leaves of the stevia plant.
Over 100 phytochemicals have been discovered in stevia. It is rich in terpenes and flavonoids. Of these eight glycosides, stevioside is considered the sweetest and has been tested to be approximately 300 times sweeter than sugar. Stevioside, comprising 6-18% of the stevia leaf, is also the most prevalent glycoside in the leaf. Other sweet constituents include steviolbioside, rebaudiosides A-E, and dulcoside A.
Stevia extracts generally contain a high percentage of the glycosides of the diterpene steviol. The leaves of stevia rebaudiana contain over 10 different steviol glycosides. Steviol glycosides are considered high intensity sweeteners (about 250-300 times that of sucrose) and have been used for several years in a number of countries as a sweetener for a range of food products. Stevioside and rebaudioside A are the principal sweetening compounds and generally accompanied by smaller amounts of other steviol glycosides. The taste quality of rebaudioside A is better than stevioside, because of increased sweetness and decreased bitterness (Phytochemistry 68, 2007, 1855-1863).
The structures and chemical abstract service registry numbers for steviol and its glycosides that are the main sweetening agents of the additive steviol glycosides are shown below:
 Compound nameC.A.S. No.R1R21Steviol471-80-7HH2Steviolbioside41093-60-1Hβ-Glc-β-Glc(2→1)3Stevioside57817-89-7β-Glcβ-Glc-β-Glc(2→1) 4Rebaudioside A58543-16-1β-Glc 5Rebaudioside B58543-17-2H 6Rebaudioside C63550-99-2β-Glc 7Rebaudioside D63279-13-0β-Glc-β- Glc(2→1) 8Rebaudioside E63279-14-1β-Glc-β-β-Glc-β-Glc(2→1)Glc(2→1) 9Rebaudioside F438045-89-7β-Glc 10Rubusoside63849-39-4β-Glcβ-Glc11Dulcoside A64432-06-0β-Glcβ-Glc-α-Rha(2→1)12Rebaudioside M 1220616-44-3(β-Glc)2-β-((β-Glc)2-β-(also known as glc-glc-Rebaudioside X)
As a sweetener and sugar substitute, rebaudioside A has a slower onset and longer duration than that of sugar, and be deemed very close to sucrose, although some of its extracts may have a bitter or licorice-like aftertaste at high concentrations. All steviol glycosides are bitter, some in less degree and some in greater degree.
The relationship between steviol glycoside mixtures, solubility, and how solubility of these mixtures affects the overall taste profile of stevia sweeteners has not been studied in detail.
Recrystallization of rebaudioside A may produce various polymorphs that can vary in of solubility. For example, U.S. Pat. No. 8,367,138 discloses rebaudioside A solubility for various forms. Form 1: a rebaudioside A hydrate; Form 2: an anhydrous rebaudioside A; and Form 3: a rebaudioside A solvate. In addition to the three polymorph forms of rebaudioside A, the purification of rebaudioside A may result in the formation of an amorphous form of rebaudioside A, Form 4.
Form 1Form 2Form 3Form 4Rate ofVery lowIntermediateHighHighdissolution in(<0.2%/60 min)(<30%/5(>30%/5(>35%/5water at 25° C.minutes)minutes)minutes)Alcohol<0.5%<1%1-3%<0.05%contentMoisture  >5%<1%<3%6.74%content
Therefore, a need for steviol glycosides or a stevia glycoside composition with superior solubility exists in the food and beverage industry.